您似乎没有为视网膜设备使用适当的比例尺.

It looks like you are not using the appropriate scale for retina devices.

ViewController.m

ViewController.m

CGContextScaleCTM(ctx, 1, -1);

这应该基于设备的规模.

This should be based off the device's scale.

例如(假设y比例值出于某种原因需要为负)

e.g. (Assuming the y scale value needs to be negative for some reason)

CGFloat scale = [[UIScreen mainScreen] scale]; 

CGContextScaleCTM(ctx, scale, -scale);